Personal Trainer's Method of Measuring Body Fat Percentage

by Courtney McCaffrey

Your personal trainer can help you determine your body fat percentage in a number of ways.

While many women fixate on that number on the scale, your body fat percentage is a much more important indicator of your physical condition. You could fall within the weight norms for your age and height and still have too much fat, or you could exceed the norms and have lots of good, lean muscle. Trainers can use a number of methods to measure your body fat percentage, but the accuracy, simplicity and expense vary. It's important to have your body fat percentage checked often to give you a better idea of your progress.

Using Skin Calipers

Many trainers use the skin fold method of finding body fat percentage because it's reliable, inexpensive and can be performed easily and often to track progress. This technique is based on the theory that about 50 percent of your body fat is under your skin. Trainers pinch skin at certain specified sites on your body and measure the skin fold with calipers. The measurements, taken in millimeters, are then summed and applied to an equation to find your body fat percentage, or your trainer may have a chart she can plug the average of the measurements into, based on your age, to determine your body fat percentage. The accuracy of this method mostly depends on how practiced your trainer is at taking the measurements.

Bioelectric Impedance Analysis

Another fast and painless way for your trainer to measure your body fat percentage is through Bioelectric Impedance Analysis (BIA). This method is based on the idea that electricity flows easily through muscles because of their high water content and that fat, with its low water content, impedes the flow of electricity. Your trainer will place electrodes on your hands and feet, and a current will be sent through your body. While it may seem creepy; it's harmless. Another device then measures your body's resistance to the flow of electricity to determine your body fat percentage. This method is considered accurate as long as the electrodes are placed correctly by your trainer, you are well-hydrated for the analysis and you haven't consumed alcohol for 24 hours prior to the BIA.

Hydrostatic Weighing

Hydrostatic weighing is considered one of the most accurate ways of measuring body fat percentage and usually comes within 1.5 percent of your actual body fat percentage. In this method, you sit in a chair that's suspended into a specialized tank of water. The seat is connected to a scale that measures your underwater weight. Your trainer will calculate your body density percentage by comparing your normal weight to your underwater weight and use this to determine your body fat percentage. The idea is that if you have a lot of bone and muscle and little fat, you will actually weigh more in water and vice versa. Not surprisingly, the equipment to run this test is expensive and not available in many gyms.

Near Infrared Interactance

According to Shape Up America, Near Infrared Interactance (NIR) was originally used by the United States Department of Agriculture to determine the body composition of livestock, but it also works on people who way somewhat less than a cow. With this method, a computerized spectrophotometer with a light probe, or wand, is used to send a low-energy beam of light to one or various sites on the body. The light passes through the fat and muscle on the site and is reflected back to the probe. Your trainer would then run the density measurements gathered by the computerized spectrophotometer through an equation to calculate your body fat percentage. Although this method is used by a lot of health centers, it's actually less accurate than the basic skin fold test.

About the Author

Courtney McCaffrey graduated from the College of Charleston in 2008 with a B.A. in media studies. She has served as an editor for Blooming Twig Books and the MADA Writing Services publishing company. She is now a writer on various outdoor sports such as snowboarding, skiing, surfing and bodysurfing.